1. Field of the Invention
The invention relates to laminated honeycomb structures, and more especially to the checking of the bonding of the cellular core of the honeycomb to a skin. In this regard the invention proposes a checking process and a specially designed device for implementing the present process.
2. Summary of the Prior Art
In what follows, a laminated honeycomb structure will simply be referred to as a xe2x80x9choneycombxe2x80x9d. Honeycombs are well known in industry, and especially in aeronautics for making in particular turbomachine seal packings, acoustic panels or for constructing thin and rigid panels such as nozzle flaps or aircraft structures. Honeycombs usually take the form of flat or shaped plates, the form of frustoconical monobloc ferrules or the form of sectors of these same ferrules. The term monobloc should be understood to mean one-piece. At this stage of manufacture the honeycomb comprises a cellular core bonded via one of its sides to a skin. The skin is a flat or bowed plate which can be of the same material as the cellular core or of a different material. The cellular core takes the form of adjacent cells separated by partitions extending in the direction of the thickness of the honeycomb, the ends of the partitions on one side of the cellular core being bonded to the skin, the cells opening out on the other side, these cells customarily being hexagonal, but sometimes rectangular, these partitions customarily being substantially perpendicular to the surface of the honeycomb, and more rarely inclined.
The making of the honeycomb comprises a tricky operation, i.e. the bonding of the cellular core to the skin, this bonding being done for example by gluing or brazing. The defects in bonding the partitions to the skin appear in an isolated manner or over an expanse grouping together several mutually adjacent cells. These defects can be an absence or a localized insufficiency of binding agent or an incipient melting of the partitions of the cells when using a binder such as a high-resistance brazing whose melting point is near that of the metallic alloy constituting the honeycomb. Such defects are manifested by the appearance on the bottom of the cells of spaces between the partitions of the cells and the skin, these spaces placing the cells in communication with one another.
In the case of hexagonal cells, the cellular core can be made from strips whose width is equal to the thickness of the cellular core, said strips each being folded to form a succession of half-hexagons, each fold constituting one of the six partitions of each hexagonal cell, said strips thereafter being disposed side by side and assembled together, each cell thereby comprising two double opposite partitions. In the case of braised honeycombs, part of the brazing used to bond the cellular core to the skin rises up by capillarity between the two partitions constituting a double partition, and effects the bonding thereof. In any event and regardless of the mode of bonding used, this bonding together of the double partitions must also be checked.
The checking of the brazing runs up against three sorts of difficulties industrially, i.e.:
a honeycomb must be able to be checked rapidly, despite the high number of its cells,
the defects are situated essentially on the bottom of the cells whilst the depth of said cells often exceeds ten times their mean diameter,
the cells may be of small sizes, with a width of less than a millimeter,
it must be possible to detect point defects involving only two adjacent cells, and not merely expanses of defects extending over several cells, or even a large number of cells.
In turbomachines, especially turboengines for aircraft, the honeycombs are mainly used as abradable seal packings between the rotating parts and the fixed parts. Cells are customarily hexagonal with a major diameter of less than 3 mm, typically 1.8 mm. Diameters dropping to 0.6 mm are envisaged. For example, a 45xc3x97145 mm frustoconical sector comprises around 3000 cells of {fraction (1/16)}th of an inch, i.e. around 1.6 mm, and a monobloc ferrule of width 45 mm and diameter 800 mm comprises around 53,000 thereof. In aircraft structures and pods, the diameter of the cells may reach 36 mm, this again representing a density of around 1200 cells per square meter.
The surface of the cellular core of the honeycomb which is opposite the skin will be referred to as the xe2x80x9cfree surfacexe2x80x9d. To simplify the language and unless specified to the contrary, the expressions xe2x80x9con the free surfacexe2x80x9d, xe2x80x9cabovexe2x80x9d etc. will be used to specify that which is outside the honeycomb on the free surface side, and the expressions xe2x80x9cunder the free surfacexe2x80x9d, xe2x80x9cbelowxe2x80x9d etc. will be used to specify that which is depthwise in the honeycomb, without prejudging the actual orientation of said free surface in space.
A widespread so-called xe2x80x9ccapillarity-basedxe2x80x9d checking process consists in filling the cells of the honeycomb with a solvent such as fluorinated trichloroethane by dipping in a vessel, in inclining the honeycomb and in visually examining its surface under black light. When cells are placed in communication via defects of bonding, liquid flows from one cell to another, and the openings of the cells concerned show up with a different intensity. This process is rapid, but nevertheless has three drawbacks:
it emits polluting vapors, especially with regard to the operator,
it demands large vessels when the panels to be checked are of large size,
it demands an additional operation of removing the liquid from the cells, this becoming problematic when the cells are of small size or else when the honeycomb is an annulus and the openings of the cells are pointing inward.
A process is also known which consists in heating the honeycomb through the side of the skin and in examining the emission of infrared from the other side, this emission being weaker in the expanses exhibiting brazing defects, since the thermal conductivity in the thickness direction of the honeycomb is lower there. This process is however reserved for honeycombs of large size, since the edge effects are important. Moreover, this edge effect masks point defects. Consequently, this process only allows detection of expanses of defects extending over numerous cells.
The patent FR-2,716,260 also granted in the United States under number U.S. Pat. No. 5,548,400 discloses a checking process consisting in strongly illuminating a cell by bringing in front of its opening an optical fiber connected to a light source, and in detecting the weak light passing through a bonding defect into the adjacent cells by bringing above said adjacent cells optical fibers connected to optoelectronic detection means, the optical fibers being held by a solid support laid on the surface of the honeycomb, this support being positioned with respect to the openings of the cells by pegs penetrating into neighboring cells. This process nevertheless has the drawback of being very low, since the instrument must be positioned in succession in front of each cell to be examined, and the use of a machine of the robot arm type would merely reduce this drawback without eliminating it. Moreover, the inaccuracy in the geometry of the cells precludes the assembling of a sizable number of instruments for checking several cells simultaneously.
Hand-held scanners which can be connected to microcomputers and make it possible to digitize a document with the aid of specialized software are also known. Such scanners comprise a light source illuminating a line on the document, an objective constructing a real image of the illuminated line, an array of photoelectric receptors disposed on the real image of the illuminated line, a sampling analog/digital converter producing a digital signal consisting of a series of doublets indicating the intensity of the signal received by each photoelectric receptor as well as the position of the receptor in the array, and means for measuring the displacement of the scanner on the surface of the document and for producing a digital signal indicating the displacement. These two digital signals are transmitted to a microcomputer equipped with specific software, said software making it possible to reconstruct the image of the document, to store this image in the chosen standard, for example in the xe2x80x9cbitmapxe2x80x9d or BMP format, and to display said image of the document on the screen of the microcomputer. The measurement of the displacement can be performed by a wheel in contact with the document, said wheel comprising toward its periphery a plurality of regularly spaced holes marching past a photoelectric receptor, said photoelectric receptor producing electrical pulses which are subsequently totalized by a counter so as to deduce the displacement thereof. The holes can be replaced by magnetized zones, and the photoelectric receptor by a magnetic reading head. In another embodiment, the displacement of the scanner is motorized, and the aforesaid wheel is disposed on a mechanical transmission connected to the motor. Even by modifying the adjustment of the objective, such scanners do not make it possible to show up the defects on the bottom of the cells of the honeycomb.
A first object of the invention is to provide a rapid and nonpolluting process for checking the bonding of the cellular core of a honeycomb to a skin.
A second object of the invention is to provide a rapid process for establishing a map of the bonding defects.
Subsidiarily, a third object of the invention is to provide a checking process which is tolerant to the geometrical irregularities of the honeycomb.
A fourth object of the invention is to provide a specially designed instrument for implementing the process for checking bonding defects.
A fifth object of the invention is to provide a specially designed instrument for implementing the process for mapping bonding defects.
According to the invention, the first object is achieved by a process for checking the bonding of the cellular core of a honeycomb to a skin, said honeycomb comprising a cellular core consisting of adjacent cells delimited laterally by partitions, said core being bonded at one side to a skin whilst at this stage of manufacture the other side constitutes a free surface here the mouths of said cells are open, said process comprising the following steps:
using a light source to illuminate a so-called illuminated zone on the free surface of the honeycomb, so as to illuminate the interior of the cells opening out into said illuminated zone; and
detecting the so-called xe2x80x9cemergentxe2x80x9d light exiting the cells in a so-called observed zone likewise on the free surface of the honeycomb,
the minimum distance between said illuminated zone and said observed zone being denoted E and defining a direction D, the distance E being at least equal to the width L1 of the mouths of the cells measured in the direction D.
The minimum distance E is taken between a geometrical point A at the edge of the illuminated zone and a geometrical point B at the edge of the observed zone, the direction D being parallel to the geometrical segment AB.
It will be understood that such an arrangement prevents the illuminated zone and the observed zone from being present simultaneously above the mouth of the same cell, this being so regardless of the relative position of said illuminated zone and of said observed zone with respect to the cells. Therefore, it is not necessary to position the illuminated zone and the observed zone above the checked partitions, it is sufficient xe2x80x9cto pass abovexe2x80x9d. Specifically, as a cell cannot be located simultaneously under the illuminated zone and the observed zone, the light emerging into the observed zone can originate only from the incident light which has passed through a defect, and not from the incident light exiting directly from the illuminated cell. Thus, when the illuminated zone and the observed zone are in a favorable position, that is to say on either side of partitions containing defects, an emergent light appears in the observed zone and can be detected by the process. In other cases, an emergent light of this kind cannot appear. Since a check can be performed at a location of the free surface of the honeycomb simply xe2x80x9cby passing abovexe2x80x9d, checks can rapidly be performed at different locations of said free surface.
The terms illumination limit and observation limit will respectively designate the limits overlooking one another of the illuminated zone and of the observed zone. The geometrical points A and B are obviously on said illumination limit and said observation limit respectively. Additionally, the illuminated zone and the observed zone need not be very extensive. A width of at most equal to E is sufficient in practice, the width of the illumination zone being taken from the illumination limit, and the width of the observation zone being taken from the observation limit.
The process forming the subject of the present invention should not be confused with the process disclosed by the aforesaid patent FR-2,716,260. Thus, in this patent the light source and the light receptor are a distance apart which is smaller than the width of the cells, so that each can be placed right opposite two adjacent cells. If said light emitter and said light receptor are not correctly positioned on the free surface of the honeycomb, they may then be simultaneously located above the same cell, the incident light illuminating a cell then being able to exit from this same cell through the observed zone and therefore to produce a false flaw signal. Accurate means of positioning, such as pegs, are therefore indispensable, thereby considerably slowing down the checking process.
Advantageously, the width E is less than the width L2 of the openings of two mated adjacent cells, said width L2 being likewise taken in the direction D. Such an arrangement makes possible the simultaneous presence of the illuminated zone above the opening of a first cell and of the observed zone above the opening of a second cell adjacent to the first, thus making it possible to detect a defect limited to the partition between these two adjacent cells. The term xe2x80x9copenings of two mated adjacent cellsxe2x80x9d should be understood to mean the assembly constituted by the two openings in the mutually relative positions which they occupy in the honeycomb. In practice, the person skilled in the art will tend to reduce the value E to as near to L1 as possible. Therefore, during the detection of a defect, a more sizable part of the illuminated cell is covered by the illuminated zone, thus making it possible to inject more light into said illuminated cell and thereby to increase the intensity of the observed light. Likewise, a more sizable part of the observed cell is covered by the observed zone, thus facilitating the detection of any emergent light. In practice, the person skilled in the art will however adopt a difference Exe2x88x92L1 which is sufficient to take into account the dimensional tolerances of the cells.
It will be noted that the tolerance of the process to the variations in the direction D is good in the case of hexagonal cells whose shape approximates to a circle. In the case where the width E is at least equal to a major diameter of the cells, the direction D may be any.
Advantageously, the intermediate zone, between the illumination and observation limits on the free surface of the honeycomb, will be covered by a mask which is opaque to light, said mask being delimited laterally by a so-called xe2x80x9cilluminationxe2x80x9d edge and a so-called xe2x80x9cobservationxe2x80x9d edge opposing one another, said illumination edge having the same shape as the illumination limit and being positioned above it, said observation edge likewise having the same shape as said observation limit and being positioned above it, said illumination edge being touched by the incident light preferably over its entire length.
Such a mask makes it possible to obstruct the stray light exiting from an illuminated cell in the intermediate zone, and thereby to permit the detection of defects of small size which therefore produce only a weak emergent light. Specifically, this emergent light being naturally weak by comparison with the incident light from which it originates, the stray light exiting directly from the illuminated cells under the intermediate zone would dazzle the means of detection of the emergent light, said means of detection then no longer being able to discern only the emergent light originating from consequent defects. By obstructing this stray light, the mask therefore enables weak emergent lights originating from smaller defects to be rendered discernible.
It will be understood that the mask cooperates with the illumination edge and the observation edge so that illumination and observation limits are rendered sharper, this making it possible to check smaller-sized cells. Specifically, the shadow cast by the mask and by the illumination edge on the free surface of the honeycomb creates the intermediate zone, the illumination limit being the projection onto said free surface of the illumination edge illuminated by the incident light. Likewise, the observation edge sharply delimits the observed zone and therefore creates the observation limit. It is also understood that the blurring of the illumination limit and of the observation limit must be weak comparatively with the width L1 of the cells. Thus, sharper illumination and observation limits therefore make it possible to check cells of smaller width.
The person skilled in the art will position the illumination edge and the observation edge against the free surface of the honeycomb or in a close neighborhood thereof. It is understood that the allowable distance between the mask and the free surface of the honeycomb is dependent on the properties of the light source and the means of detection of the emergent light. Thus, in the case where the light source and the means of detection are hardly directional, the mask will have to be practically in contact with the free surface of the honeycomb. Conversely, in the case where the light source and the detection means are directional, it becomes possible to distance the mask from the free surface and to thus improve the tolerance of the process to irregularities of said free surface. In practice, a distancing at most equal to 2xc3x97E will be adopted, i.e. of between zero and twice the width E of the mask, so that the mask retains sufficient effectiveness.
In what follows and so as to simplify the language, the term xe2x80x9cin front of the maskxe2x80x9d will denote that which is on the same side of the mask as the honeycomb, and xe2x80x9cbehind the maskxe2x80x9d that which is on the other side.
Advantageously, the incident light supplied by the light source is substantially perpendicular to the free surface of the honeycomb. Such an arrangement enables the position of the illumination limit on the free surface of the honeycomb to be kept substantially constant with respect to the mask, this despite any variations in the distance between the mask and the free surface, said variations originating from irregularities of said free surface. Thus, the tolerance of the process to geometrical irregularities of the free surface is improved, as is the capacity of the process to check smaller-width cells.
Advantageously, the illumination limit and the observation limit extend over N consecutive cells, N being at least equal to three. Such an arrangement extends the check to N consecutive cells between said illumination limit and said observation limit, said check of the N cells remaining simultaneous, and therefore makes it possible to accelerate the checking of a honeycomb. In practice, the person skilled in the art would use values of N at least equal to 15 or even 50 or more, so as to simultaneously check a larger number of cells, N being limited only by the irregularities of the free surface of the honeycomb and by the capacity of the means used to tolerate said irregularities.
Advantageously, the illumination limit and the observation limit are moved together along a geometrical line of displacement at the free surface of the honeycomb. Such an arrangement makes it possible to check by scanning the cells situated along the geometrical line of displacement, and thereby to accelerate the check. The term xe2x80x9cmoved togetherxe2x80x9d should be understood to mean that they retain their relative positions with respect to one another during the movement. It is in fact understood that there is no longer any need to position the illumination limit and the observation limit on either side of each of the partitions of the cells along the geometrical line of displacement. The check can be performed according to a continuous scan, the process making it possible to detect any defect when the illumination limit and the observation limit arrive in a favorable position, that is to say on either side of a partition, the process detecting nothing but not producing any false signals in the converse case either.
In a preferred embodiment of the invention, the illumination limit and the observation limit extend over N consecutive cells, N being at least equal to three, said illumination limit and said observation limit being moved together along a geometrical line of displacement at the free surface of the honeycomb. Such an arrangement makes it possible to check in a single scan the geometrical surface generated by the joint displacement of the illumination limit and of the observation limit along this geometrical line of displacement, and hence to accelerate the checking of the brazing of the honeycomb. It will be understood that the speed of the check is proportional to the product Nxc3x97V0, V0 being the speed of displacement along the geometrical line of displacement.
In a first embodiment of the invention, the space above the observed zone is cleared, and the detection of the emergent light is visual. This process has the advantage of simplicity but it must be reserved for occasional checks owing to the fatigue which it would otherwise impose on the operator. The operator can also observe the emergent light through an optical magnifying glass, especially in the case where the cells are small. In the case where the intermediate zone extends over a sizable number of cells, the magnifying glass can be cylindrical.
According to the invention, the second object is achieved by a process for checking the bonding of the cellular core of a honeycomb to a skin, the illumination and observation limits extending over N consecutive cells, N being at least equal to three, said illumination and observation limits being moved together along a geometrical line of displacement at the free surface of the honeycomb, the process being noteworthy in that:
the joint displacement of the illumination limit and of the observation limit along the geometrical line of displacement is measured,
the positions of the emergent light appearing along the observation limit are marked,
the appearances of the emergent light are indicated on a system of coordinates X,Y, the measurement of the displacement being plotted on one of the coordinates X,Y and the corresponding positions of the emergent light being plotted on the other coordinate Y,X.
It will be understood that the process thus makes it possible to generate point by point the map of honeycomb bonding defects.
According to the invention, the third object is achieved by a process for checking the bonding of the cellular core of a honeycomb to a skin, the process being noteworthy in that the observed zone is continuous, in that a real optical image of the observed zone is constructed with the aid of an objective, and in that the emergent light is detected on the basis of said real optical image. Such an arrangement makes it possible to separate the emergent light from any stray lights, and thereby substantially to increase the tolerance of the system to irregularities of the free surface of the honeycomb and to said stray lights. It will in fact be understood that the real optical image shows up the emergent light passing through the brazing defects in the form of small light spots which are sharper or less sharp according to the adjustment of the objective, the brightness of said spots being considerable because the objective naturally concentrates the emergent light. On the real image, these light spots are then more easily distinguished:
from the stray lights illuminating the observed surface, for example by passing between the free surface of the honeycomb and the mask, these stray lights reproducing the design of the cells more or less sharply on the real image,
from the stray lights generally arriving at the objective and dispersing as a low-intensity general fog on the real image with respect to the light spots representing the defects.
Combined with an incident light perpendicular to the free surface of the honeycomb, the process makes it possible to tolerate without difficulty a discrepancy, between the free surface of the honeycomb and the mask, of as much as twice the width E of the mask. The permanent physical contact between the mask and the free surface of the honeycomb is therefore not necessary.
In a particular form of implementation of the process, the objective is accommodated on the bottom of the cells, so as to give a sharp image of the defects.
According to the invention, the fourth object is achieved by an instrument for checking the bonding of the cellular core of a honeycomb to a skin by the process of the invention, said instrument comprising:
a) an opaque mask delimited laterally by an illumination edge and an observation edge opposite said illumination edge,
b) a light source disposed at the rear of the mask, said light source being secured to the mask, said light source producing an incident light beam going from the rear of the mask to the front of the mask, said beam being partially cut by the mask and the illumination edge, said mask thus extending partially outside the beam on the observation edge side, said observation edge itself being outside said beam,
c) means for detecting any emergent light going from the front to the rear of the mask, and therefore in the opposite direction to the incident light, said detection means being disposed behind the mask, and therefore on the same side as the light source said detection means being secured to the mask, said emergent light passing in front of the observation edge in the neighborhood thereof,
wherein at M successive geometrical points A on the illumination edge and at M successive geometrical points B on the observation edge, M being at least equal to five, the distance AB between the illumination edge and the observation edge is a minimum and equal to E, the distance D1 between two geometrical points A being at least equal to 0.5xc3x97E, the distance D2 between two geometrical points B also being at least equal to 0.5xc3x97E, the M geometrical points A forming an open line whose two geometrical points A situated at its ends are a distance apart greater than that of any other doublet of geometrical points A, the M geometrical points B likewise forming an open line whose two geometrical points B at its ends are a distance apart greater than that of any other doublet of geometrical points B.
It will be understood that the position of the light source and of the means of detection of any emergent light define the so-called xe2x80x9crearxe2x80x9d side of the mask, said light source and said means of detection both being at the rear of the mask, the honeycomb to be checked being disposed xe2x80x9cin front ofxe2x80x9d the mask, said light source possibly however protruding laterally from the mask on the illumination edge side, said means of detection likewise possibly protruding laterally from the mask on the observation edge side.
It will be understood that the mask can be disposed flat on a larger surface than itself or in the neighborhood of this surface, said surface possibly being the free surface of a honeycomb. The light source makes it possible to illuminate this surface from the rear of the mask over a so-called illuminated zone, said illuminated zone being delimited by a sharp edge or xe2x80x9cillumination limitxe2x80x9d produced by the shadow cast by the mask and by the illumination edge on the surface. The means of detection of any emergent light make it possible to observe from the rear of the mask a so-called observation zone on the surface, said observation zone being delimited by a sharp edge, the so-called xe2x80x9cobservation limitxe2x80x9d, produced by the mask and the observation edge. The mask obstructs any light susceptible of passing between the illumination edge and the observation edge. Therefore, a weak emergent light passing in front of the observation edge can be easily detected.
It will be understood that the assembly consisting of the mask, the light source and the means of detection of any emergent light can be displaced parallel to the surface against which the mask is disposed. To allow this, the mask is obviously free of any forward projecting object, said objects being susceptible of obstructing such a displacement. This displacement can be performed by any means, including by hand.
It will be understood finally that the characteristics according to d) above make it possible to lengthen the mask to a length D2 without modifying its width E, hence the size of the cells susceptible of being checked. Thus, when the mask+light source+detection means assembly is displaced parallel to the free surface of the honeycomb, a more sizable surface containing proportionally more cells is scanned in the same amount of time, thus increasing the speed of checking. It will also be understood that this characteristic does not exclude the presence of more closely spaced geometrical points A or B. For example, when the illumination edge and the observation edge are two continuous, parallel lines, there exists an infinity of series of points each satisfying this characteristic.
In practice, a light source whose width is at most equal to the width E of the mask is sufficient, said width of the light source being taken from the illumination edge. It will be understood that it is conversely important that the incident light beam to touches the illumination edge so as to be partially cut by the mask, this making it possible to generate a sharp illumination limit by projection on the free surface of the honeycomb. It will also be understood that the detection means need not detect any emergent light very remote from the observation edge. It is sufficient for these detection means to be able to detect any emergent light passing at a distance at most equal to the width E of the mask. It will be understood finally that the adjustment of the actual position of the emergent light thus detectable is dependent on the honeycomb and on the characteristics of the instrument.
Advantageously, M will be at least equal to fifteen, or even fifty, when the regularity of the free surface of the honeycomb so permits. The person skilled in the art will then set the width E to a value slightly greater than the maximum width L1 of the cells having regard to the manufacturing tolerances and to the maximum possible distancing of the mask from the free surface of the honeycomb, this distancing making it possible to absorb the irregularities of said free surface.
The present invention ought not to be confused with the checking instrument disclosed by patent FR-2,716,260 according to the description and Figure four of said patent. Specifically:
1. Figure four shows an illuminating optical fiber 40 and two observing optical fibers 42 disposed on either side of the illuminating fiber 40. What could correspond to the illumination edge and to the observation edge, according to the present invention, consequently comprises just two diametrically opposed geometrical points A on the illuminating optical fiber 40 and two geometrical points B on the observing optical fibers 42 for which the distance E is a minimum, unlike the present invention for which the geometrical points A and B are each at least five in number.
2. The distance D1 between the two geometrical points A is equal to the diameter of the illuminating optical fiber 40 and seems in Figure four to be actually greater than 0.5xc3x97E. However, this is fortuitous, since the fatness of this optical fiber does not play any part and is not even mentioned in the description of the cited patent.
3. Since the cells of a honeycomb can only comprise three, four or six sides, it is strictly speaking possible to imagine that the instrument presented by way of state of the art can have an illuminating fiber 40 and up to six observing fibers 42, hence up to six points A and six points B according to the vertices of two regular hexagons. However, only four points out of the six constitute an open line whose two extreme points are at a distance greater than that of any doublet of geometrical points A, whilst according to the present invention, there are at least five thereof.
4. Moreover, this cited patent does not in any way suggest open and thus outspread lines making it possible to scan a wider surface, since if there are six geometrical points A or B, these can only form closed lines, and since this scanning is made impossible by the presence of the pegs 45, said pegs constituting an essential means for centering the optical fibers 40, 42 above the cells. Moreover, this necessity of centering the optical fibers above the cells makes it impossible to use a large number of optical fibers to simultaneously check a large number of cells, on account of the inevitable dimensional manufacturing tolerances for the cells. The present invention, conversely, does not have these limitations. As will also be noted, that which may correspond, in the prior document, to the illumination edge and to the observation edge play no part in this prior document.
In practice, the minimum width E of the mask is at most equal to 36 mm so as to check the honeycombs customarily manufactured in industry. In the case of seal packings in turbomachines, E is less than 3 mm. This minimum width E can drop to values of between 0.6 mm and 1 mm so as to be able to check the honeycombs envisaged in the future.
It will be noted that the illumination edge and the observation edge can be split or continuous, as will be shown by two particular embodiments of the invention, set out later.
Advantageously, the incident light and the emergent light facing said incident light make an angle xcex1 of less than 10xc2x0, and preferably less than 5xc2x0. Such an arrangement makes it possible to reduce the variations in the distance between the incident light and the emergent light when becoming distanced from the mask, this distance being taken parallel to the mask. As a result, the tolerance of the instrument to irregularities of the honeycomb free surface against which this instrument is applied is substantially increased. Specifically, if we consider a segment AB corresponding to a minimum width of the mask, it will be understood that the distance between the projections onto said free surface of the geometrical point A according to the incident light and of the geometrical point B according to the direction of the emergent light varies only very slightly when said free surface is distanced slightly from the mask on account of the manufacturing irregularities which it contains.
The term xe2x80x9cemergent light facing said incident lightxe2x80x9d should be understood to mean that the emergent light is geographically at the same level as the incident light along the mask, in other words that it would be susceptible of originating from said incident light. In practice, the incident light and the emergent light are substantially perpendicular to the mask and converge at the front of said mask.
In a particular embodiment, the mask is flexible in a direction perpendicular to said mask. With such an arrangement, the mask can automatically take the shape of the surface against which it is susceptible of being applied. This arrangement is more particularly intended for surfaces of variable curvature with wide cells, such as the structures of pods or of reversers surrounding turbojet engines.
Advantageously, the instrument comprises an opaque screen, for example a plate, disposed between the light source and the means of detection of the emergent light. Such a screen makes it possible to obstruct any stray light coming from the light source and susceptible of reaching the detection means, thereby facilitating the detection of any emergent light which is much weaker than the incident light.
Advantageously, such a screen extends up to the mask and arrives at this mask from the rear, between the illumination edge and the observation edge, so as to obstruct any stray lights originating from the light source and being susceptible of reaching the observed zone, thereby further facilitating the detection of any emergent light which is much weaker than the incident light.
In a particular embodiment of the instrument which is more particularly reserved for the checking of cells of small width, the mask is integral with the screen and constitutes a lip thereof. It will be understood that the illumination edge and the observation edge are then constituted by the corner which the lip forms with each of the faces of the screen. In practice, in the most frequent case where the cells are perpendicular to the free surface of the honeycomb, the lip is perpendicular to the screen and the screen is positioned above the cells perpendicularly to the free surface.
The invention proposes an instrument of the hand-held scanner type, that is to say an instrument allowing checking by scanning and capable of being held in the hand. Such an instrument is noteworthy in that it comprises:
a soleplate which is opaque to light and drilled in the thickness direction with a row of at least five illuminated holes and with a row of at least five observed holes parallel to the row of illuminated holes and separated from it by the mask and the screen both integral with said soleplate,
a light source split into a plurality of elementary light sources, for example LEDs, each of said elementary light sources being disposed at the rear of an illuminated hole and projecting an incident light through said illuminated hole,
elementary detection means, for example photodiodes or phototransistors, converting the light into electric current, each of said elementary detection means being disposed at the rear of an observed hole and receiving an emergent light passing through said observed hole,
indicator lights, visible from outside the scanner,
a plurality of amplifiers each associated with a continuous background separator, each assembly of amplifier+continuous background separator being connected to P greater than =1 elementary detector and to an indicator light.
It will be understood that the opaque soleplate makes it possible to rub the hand-held scanner on the free surface of the honeycomb, such a scanner obviously being free of any element projecting forward from the soleplate and susceptible of blocking the displacement of the scanner according to a movement parallel to the free surface of the honeycomb to be checked. It will be understood that the mask is constituted by the part of the surface of the soleplate between the illumination holes and the observation holes, and that the screen is constituted by the volume of the soleplate between said illumination holes and said holes. It will likewise be understood that the soleplate optically isolates the elementary detection means from the ambient light, doing so during the use of the scanner.
Such an instrument also operates with one, two, three or four illumination holes and with one, two, three or four observation holes. However, the inventor agrees to limit the scope of the claim to five holes or more, so as to remain consistent with the general characteristics of the instrument forming the subject of the invention.
Advantageously, the indicator lights are disposed in line and substantially at the rear of the mask, so as to directly signal the locations where the defects are detected.
According to the invention, the fifth object is achieved by an instrument for checking the bonding of the cellular core of a honeycomb to a skin, said instrument being specially designed to implement the present process, said instrument being noteworthy in that it comprises:
a) at least one chamber of photographic type equipped with an objective and with an array of photoelectric receptors, said chamber constituting the means for detecting the emergent light, said objective being situated at the rear of the mask and pointed substantially at the observation edge, the geometrical axis of said objective being substantially orthogonal to said observation edge and forming with the screen an angle of incidence xcex2 of less than 10xc2x0, said objective forming in the chamber a real image of the space in the neighborhood of the observation edge viewed from the rear of the mask, said real image consequently comprising the real image of the observation edge viewed from the rear of the mask, and the off-mask real image of the space in front of the observation edge likewise viewed from the rear of the mask, the array of photoelectric receptors being disposed on the off-mask real image, parallel to the real image of the observation edge and in practice in the neighborhood of said real image of the observation edge,
b) a sampling analog/digital converter whose input is connected to the photoelectric receptor array and whose output is connected to a calculator, said converter examining the photoelectric receptors and producing a digital signal of the defects, said digital signal consisting of doublets indicating the signal intensity received by each photoelectric receptor and the position of said photoelectric receptors on the array of photoelectric receptors,
c) means for positioning and marching the honeycomb against the mask one in relation to the other, that is to say in a direction of relative travel that is substantially parallel to the mask and preferably, although not necessarily, perpendicular to the illumination and observation edges,
d) means for measuring the relative displacement of the honeycomb in front of the mask, said displacement measurement means being likewise connected to the calculator and supplying a digital displacement signal,
e) mapping software associated with the calculator, said software constructing a map of the defects on the basis of the digital signal of the defects and of the digital displacement signal.
The term xe2x80x9cchamber of photographic typexe2x80x9d should be understood to mean a space protected from ambient light making it possible to form an image on a surface with the aid of an optical objective. The actual distance from the array of photoelectric receptors to the real image of the observation edge is adjusted in practice by slightly modifying the orientation of the chamber, this distance having to be equal to dxc3x97r, d being the distance between the observation edge and the emergent light to be detected, and r the reduction ratio the observation edge and its real image given by the objective at the back of the chamber.
In practice, the calculator will be a computer and the mapping software will be software customarily used to scan images. It will thus be understood that the map of the defects can be instantaneously displayed on a screen of the computer, printed and/or stored on a magnetic medium automatically or on request. The image thus digitized can also advantageously be reprocessed, for example:
so as to show up the defects in black on a white background, so as to make the map more readable,
so as to erase the design of the cells, in order to retain only the representation of the defects and thus to facilitate the visual examination of the map of the defects,
so as to automatically identify the good or bad pieces.
The invention will be better understood and the advantages which it affords will become more clearly apparent from the following detailed description of the preferred embodiments and with reference to the accompanying drawings. It will be noted that for the sake of clarity of the drawings, the cells of the honeycomb are in general greatly magnified with respect to the exterior means.